In stamping technology, stamping tools are used which essentially comprise an upper tool part and a lower tool part. Into these tool halves, the forming parts, the punch and the die, are arranged. Between the forming parts, a material to be processed as semifinished material is stressed beyond its yield point with the objective being to manufacture a given number of identical work pieces from it. The manufacturing accuracy of these work pieces produced by forming and cutting depends on the shape and the dimensional accuracy of the tool. In addition to the accuracy of the stamping tool achieved in production, however, the shape and dimensional accuracy of the stamped parts are also determined by the manner in which shear forces occuring during the stamping are taken up. Relative motions of the shaped parts in the horizontal direction relative to each other should be minimized.
In order to take up shear forces which occur in the stamping operation and which can lead to relative horizontal relative motions of the tool parts, stamping tools in the past have been equipped with guides for the tool halves which hold the forming parts. By these guides, the tool halves were likewise positioned relative to each other.
Of these known tools, there are at least three types: tools with plate guidance; tools with column guidance; and tools with changing frames.
Tools with plate guidance have a guiding plate firmly connected to the lower part of the tool which takes over the guidance of the punch and the positioning of the tool halves. In these tools, the punches must not leave the guiding plate due to the press stroke.
Tools with column guidance are constructed either from a column frame or from plates into which the columns are worked. In this way, the guidance and positioning of the tool halves are transferred to two or more columns. In addition to the tool guidance, the design can be further completed by a spring-loaded punch guiding plate within the tool, especially in composite sequential tools with large shear forces.
Tools with changing frames have their exchangeable tool halves inserted into a changing frame which takes over guidance and positioning. Accurate correlation of the tool halves and thereby the forming parts is provided only in the changing frame.
In all of the above known tools, however, the comparatively large amount of technical means, corresponding with high tool costs, is a problem.
Besides guided tools, so called guideless tools are also already known. In guideless tools, the separate tool halves are not themselves guided (i.e. constrained by guiding posts, for example). Rather, only the press table and press plunger are guided. In German Patent 27 11 696 a precision cutting tool with a movable plunger and a fixed table for punch preses for cutting-out sheet metal parts is described. The active tool part (the punch and the cutting plate) are accurately guided relative to each other by at least two closed linear guides which are arranged outside the tool and are in engagement near the operating plane. Each linear guide has two elements, a guiding column in a guiding sleeve, and one of these elements is connected to the plunger and the other one to the table. Such a stamping tool can supplement an automatic stamping press according to German published Unexamined patent application 22 41 639.
It is, however, a problem with the above-mentioned guideless tools to adjust the tool halves when setting tools for the first time or when changing tools. This could be done only by specially trained personnel, so that to date, such guideless tools have not found wide acceptance in practice.
It is therefore an object of the invention to provide an automatic precision stamping press in which guideless tools can be used and exchanged without problem.
This and other objects are achieved by the present invention by providing an automatic stamping press comprising a press plunger, a press table and an exchangeable guideless tool having separate tool halves with an upper tool fastenable to the press table. Guiding columns and corresponding guiding sleeves accurately guide outside the tool halves the press plunger and the press table. There are separate mounting plates, with the tool halves being respectively fastened to one of the mounting plates. Positioning devices engage the mounting plates, with at least one positioning device for each mounting plate operating to respectively position the upper tool part at the press plunger, and the lower tool part at the press table. The positioning devices are hydraulic clamping plugs that are arranged on a diagonal of each of the mounting plates. Also provided is a method for operating the automatic precision stamping press.
It is important to have a diagonal mobility in the mounting plates which can take up the thermal stresses of the tool halves. This will be realized alternatively by an oval cross-section of one of the hydraulic clamping plugs or a slide element which is movable in the diagonal direction. Latter could be a dove-tail or a lever with a roller-bearing free from backlash on which the plug is linked.
By the invention, the accuracy of plunger guidance of the automatic precision stamping press is now utilized for the first time. Thereby the guidance of the stamping tools can be replaced by the guidance of the press plunger consisting of guiding columns and guiding sleeves as compared to the press table, which is already known per se but has not found acceptance in practice because of the time-consuming positioning.
On the other hand, an automatic stamping press is provided by the invention having a positioning and clamping system which permits clamping of the two tool halves of the guideless tools so exactly that the guiding behavior of the plunger is fully transferred to the tools. Thereby, the problem is solved as to how the tool halves containing the forming parts can be positioned relative to each other in a machine tool which generates the cutting and deformation forces and takes up the shear forces occurring in the process, and thereby the relative motion mentioned at the outset can be minimized in cooperation with the features of the machine tool. A tool change can now be performed with extremely short machine shutdown times.